1. Field of the Invention
This invention relates to an improvement in an internal combustion engine that has a main combustion chamber equipped with an intake valve and an exhaust valve, and an auxiliary combustion chamber with no intake valve.
This invention further relates to a torch ignition type internal combustion engine, and more particularly to a torch ignition type internal combustion engine which has no intake valve in the auxiliary combustion chamber but is capable of effectively purging exhaust gases therefrom to ensure improved ignitability.
It is well known in the art to burn a rather lean air-fuel mixture in the engine cylinder in order to reduce the toxic components such as carbon monoxide, hydrocarbons and nitrogen oxides which are usually present in the engine exhaust. A lean air-fuel mixture, however, has inferior ignitability and flame propagation velocity, and allows raw air-fuel mixture to blow by to the exhaust manifold resulting in a reduction of the cyclic thermal efficiency.
2. Description of the Prior Art
In order to overcome the afore-mentioned difficulty, there has been introduced the so-called torch ignition type internal combustion engine which has a main combustion chamber with an intake valve and an exhaust valve, and an auxiliary combustion chamber with an intake valve, the engine being adapted to supply a lean air-fuel mixture to the main combustion chamber and a relatively thick or rich mixture to the auxiliary combustion chamber through the respective intake valves. In such an engine system, the relatively rich air-fuel mixture in the auxiliary combustion chamber is first ignited and burned, the flames bursting out from the auxiliary chamber subsequently igniting the lean air-fuel mixture in the main combustion chamber. This internal combustion engine with an intake valve in the auxiliary combustion chamber is advantageous in that it ensures combustion of the lean air-fuel mixture and high flame propagation velocity. On the other hand, such internal combustion engine invariably has a complicated construction due to the provision in the auxiliary combustion chamber of the intake valve which requires a complicated valve operating mechanism for opening and closing the same in predetermined timing.
The present inventors have previously proposed a torch ignition type internal combustion engine which comprises a main combustion chamber with an intake valve and an exhaust valve, an auxiliary combustion chamber with no intake valve, a passage intercommunicating the main and auxiliary combustion chambers, and an ignition plug having its sparking electrodes located in the auxiliary combustion chamber and in the vicinity of the intercommunicating passage. In this torch ignition type internal combustion engine, a lean air-fuel mixture inhaled into the main combustion chamber through the intake valve during the intake stroke of the piston is urged into the auxiliary combustion chamber during the succeeding compression stroke through the passage intercommunicating the main and auxiliary combustion chambers. With only fresh air-fuel mixture surrounding the sparking electrodes of the ignition plug which is located in the auxiliary combustion chamber in a position near the passage, the lean air-fuel mixture within the auxiliary combustion chamber is ignited and burned without material interference from exhaust gas which might still be remaining in the auxiliary chamber, followed by ignition of the lean air-fuel mixture in the main combustion chamber by the flames bursting out from the auxiliary combustion chamber.
With the above-described torch ignition type internal combustion engine with no intake valve in the auxiliary combustion chamber, it is necessary to purge the exhaust gases which remain in the auxiliary combustion chamber as otherwise the remaining exhaust gases would impair the ignitability of the combustible mixture.